1. Field of the Invention
The present invention relates generally to high-purity silicon single crystal growth method and apparatus, and more particularly to a method of and an apparatus for producing a single crystal from a polysilicon rod by a one-pass zoning of the floating-zone (FZ) method.
2. Description of the Prior Art
The FZ method and the Czochralski (CZ) method have been used as methods of growing single crystals of silicon. The FZ method, due to its capability of growing high purity silicon single crystals with little contamination of oxygen and others than ones grown by the CZ method, is particularly useful to produce high resistivity silicon single crystals for fabricating high-power semiconductor devices.
In the production of a silicon single crystal by the FZ method, a polysilicon rod is used as a raw material. The polysilicon rod is produced from trichlorosilane deposited on a silicon core rod in vapor phase to such an extent that the grown polysilicon has an average grain length of 10 to 1000 .mu.m. To grow single crystal, one end of the polysilicon rod is shaped into a conical form and the tip of the conical end is melted and fused with a seed crystal. Then, polysilicon rod and the seed crystal are united together while eliminating dislocations by forming a bottle neck. A silicon single crystal is grown by recrystallizing a molten silicon. The molten zone, formed by heating the polysilicon rod partially with an annular induction heating coil, is passed from the seeded end of the polysilicon rod to the other end by moving down the polysilicon rod and the grown single crystal simultaneously relative to the induction heating coil, while rotating the polysilicon rod and the grown single crystal with a concentric or an eccentric mode.
According to the prior FZ method, production of silicon single crystals by a one-pass zoning is hardly achievable. Accordingly, the conventional FZ method for producing the silicon single crystals requires a two-pass zoning, i.e., the "pre-zoning" and "dislocation-free zoning". At the first zoning of the FZ method, called "pre-zoning", an intermediate polysilicon rod is formed, and at a the succeeding FZ growth run, called "dislocation-free zoning", the intermediate polysilicon rod is converted into a silicon single crystal ingot. It was ineffective for a silicon single crystal production to apply the two-pass zoning process.